Profiling is the only true answer. If the inputs of a shader change, or the outputs: permutation is needed. And this is often: think a variant with vertex colo

Profiling is the only true answer. If the inputs of a shader change, or the outputs: permutation is needed. And this is often: think a variant with vertex colors for wind impact on vertices. Or a variant with normal map vs without. Your uniform and vertex attributes should also be as small as possible (when aligned) for the use. You never want to be sampling a zero-texture in order to have generic shader code as sampling is very expensive. I hope this helps a bit, I am no expert in this field.